For each simulation in the testing data set we estimate the Eulerian density field using a cloud-in-cell (CIC) particle mesh assignment on a grid with \(1024^3\)  voxels. At the voxel centered on position \(\mathbf {x}\) , we sum the CIC particle weights to obtain the effective number of particles \(n(\mathbf {x})\) , and then determine the overdensity \(\delta _{\mathrm {m}}(\mathbf {x}) = n(\mathbf {x}) / \bar{n} -1\)  with respect to the mean number of particles per cell \(\bar{n}\) . We Fourier transform the density fields using FFTW3 [1]} and deconvolve the CIC window function, yielding the density modes \(\delta _{\mathrm {m}}(\mathbf {k})\) . We then compute the density power spectrum \(P_{\mathrm {mm}}(k)\) , given by
\(\langle \delta _{\mathrm {m}}(\mathbf {k}) \delta _{\mathrm {m}}(\mathbf {k}^{\prime }) \rangle = (2\pi )^3 \delta ^{3}_{\mathrm {D}}(\mathbf {k} + \mathbf {k}^{\prime }) P_{\mathrm {mm}}(k) \, .\) 
